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New paper Published

A paper about collective energy gap of preformed Cooper pairs published in Nature Physics

April 12th, 2018

A paper about heterostrain in twisted graphene layers is published in Phys. Rev. Lett.

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Intervalley scattering in SOI quantum wells

A collaboration with Bath university (UK), NTT BRL (Japan) and Tohoku University (Japan)

Whether or not electrons confined to two dimensions conduct electricity when the temperature approaches absolute
zero remains a subject of intense research and controversy. It is well established that the “metallic behavior” is stronger
in systems like silicon where valley degeneracy enhances interactions. However, little is known about the role of valley splitting
and inter-valley scattering, two processes associated with valley degeneracy. After demonstrating that valley splitting could be electrically
controlled in Si quantum wells on insulator (SOI), we have recently shown that valley splitting suppresses the metallic behavior in Si
(see the page dealing with valley splitting). Here, we have addressed the problem of inter-valley scattering which has previously
been disregarded because of the lack of theoretical description.

We have implemented a recent theory of weak-localization magneto-conductivity (MC) with inter-valley scattering (see Kunstevich et al.
in Phys Rev B (2007)) to extract the inter-valley scattering time in our sample. Doing so not only allows us to demonstrate that the
metallic behavior can be observed even in presence of strong inter-valley scattering, but also to show that this observation
can be quantitatively explained by the interplay of electron-electron interactions and weak localization. Interestingly, weak localization
is canceled by the diffusive part of interaction corrections to conductivity leaving a paradoxical linear ballistic like temperature dependence
which had remained largely overlooked but is now clearly explained.

More importantly, our analysis reveals that interactions are much stronger in SOI due to the reduced screening. This could lead to a
renewal of the subject as it should allow reaching regimes of interactions which were previously unaccessible experimentally in Si.